Posted
by
timothy
on Saturday May 16, 2009 @10:36PM
from the ad-astra-per-alia-porci dept.

GvG was one of several readers to point out this "incredible photo clearly showing the silhouette of Atlantis and the Hubble Space Telescope as they passed in front of the Sun was taken Wednesday, May 13, 2009, from west of Vero Beach, Florida. The two spaceships were at an altitude of 600 km and they zipped across the sun in only 0.8 seconds." The image is all over the Web now, for good reason.

..of course it's all a trick of perspective. Being able to see them at all against the sun is about as accurate as holding your hand up to your face and squishing the sun between your fingers.

Not sure what you mean by "accurate" here. True, a silhouette is not a view the unprotected human eye could ever see (except maybe against a brown dwarf) due to the brightness, but an alien eye, filtered eye, or camera could capture such perspective. I have a little sun filter that allows me to stare directly at the su

Your understanding seems off -- the picture we're discussing is a photograph in every sense. "Trick of perspective" is an odd way to speak of it, since the perspective is simply that as visible from the ground, where the photo was taken.

more to the point: why does the brightest object in the solar system have nice shading effect to make it look spherical?

I accept that this photo has been certified legit, but that shading screams fake to me because the sun should only look like a flat disc. So the question I'm asking astronomers is to explain why the sun appears spherical instead of like a big flat bright disc?

I don't know *why*,
but that is indeed what the sun looks like if you watch it heavily filtered in a telescope,
or use a telescope to project it on a surface.

The edge like that because you see a shallower, thus cooler, portion of the sun's photosphere. As a cooler source of blackbody radiation, it looks darker and more orange. The phenomena is called limb darkening.

A sphere has more of its surface pointing directly at you near whatever point you see as the center. As your eye moves towards the edges more and more of the surface is pointing more and more away from your eye, and thus less light is emitted to your eye and it appears less bright. As the sun is SO bright that you cannot look at it, or notice the difference in brightness, without a huge amount of filtering you will only see this effect if you look at a photo, or through a telescope, with a huge filter made

We see spherical objects as spherical because of the shadows and light reflected from it causing different intensities of light reaching our eyes from it.

The sun is different, it has no shadows or light landing on it. It is the light source. If you assume that the sun is a black body of a constant temperature across its surface, the light reaching us from anywhere on its surface is constant which would make it appear to be a completely flat disc. This effect is due to two cos(theta) terms cancelling each other out if you want to do the maths and would be true no matter what the shape that the sun (or any perfect black body) actually was. If for example, the sun was a cube, we would just see the silhouette of the cube as a flat surface and none of the sides.

Now, in reality, the sun isn't a perfect black body of constant temperature and is both less dense and cooler at the edges than at the centre. This makes the edges darker and makes it look more like a spherical object. The post below on limb darkening gives the details.

Seen from the Earth the size of the Moon and the Sun appear roughly the same. In the clip you link to, the diameter of the Moon appears to be just one sixth of the Sun. Doesn't that mean it would have to have been taken about 2 million kilometers from the Moon? Do we actually have satellites in that high orbit? Or is the effect caused by something else?

Yes. The STEREO-B satellite is in a heliocentric orbit (i.e., centered on the Sun, not the Earth) outside the Earth's orbit, gradually getting farther behind it because the period of an orbit increases with distance from the Sun. That picture was taken early in the flight, when the geometry still permitted seeing the Moon and Sun in line; it won't happen any more.

Its partner, STEREO-A, is in an orbit inside the Earth's, and gradually getting ahead for the same reason. As the two diverge, they can image the Sun simultaneously and take 3-D pictures of it.

My first thought was "oh geez! with all the camera technologies we have these days, that's the best we could get??" I want voyeuristic photos of naked female astronauts with 0-g boobs. Give us some serious zoom!

Pah, if you want to feel more insignificant, hop on over to images.google.com and look at (in order): "globular cluster", "M31 Andromeda", "M31 Andromeda +halo", and "Hubble Ultra Deep Field" (HUDF).

Bear in mind that when you see a spiral galaxy in HUDF or in the deeper part of the M31 Andromeda halo deep exposure, you are seeing a galaxy about the size of M31, with about a trillion stars about the size of the one in the picture that is already making you feel insignificant relative to the "greater univers

Very much agreed. That is what is completely amazing to me... when you consciously put the view into perspective the scale becomes awe inspiring.

I never cease to be humbled whenever I catch a glimpse of how insignificant we really are. In turn I am also equally inspired by the idea that one of the smaller things in the universe, namely 'us', is also capable of beginning to comprehend it.

Yes, who would have thought that the Sun, the star around which would rotate, would be SOOOOO much bigger than a space vehicle and a space telescope. Next thing you know we'll have pictures showing how tiny people and cars look seen from space compared to the hugeness of Earth.

I find the most eye opening fact is that the sun is 93,000,000 miles behind the shuttle. It is an awesome display of the scale of the sun.

Actually we know all the distances so we can calculate how much bigger should the sun look than the shuttle in this picture.

Distance from Sun =1.496 x 10^11 m
distance form hubble=5.59*10^5
size of the sun=4.37*10^9
size of shuttle=5.6*10
Simple math says that the sun should look 291 times bigger, but this assumes that the sun was right on top when the picture was taken and that the shuttle was in horizontal position.

NASA can upgrade their equipment with a fuel scoop, which allows raw fuel to be skimmed from the surface of stars - a dangerous and difficult activity - and collecting free-floating cargo canisters and escape capsules liberated after the destruction of other ships.

When seeing a picture of a two-thousand ton manned space ship next to a space telescope with a huge nanometer accuracy mirror being repaired by a crew of people in space suits all whizzing through space with a class G star looming in the background, "simple" was not exactly the first thing which came to my mind.

I don't think I've seen a transit like this that is of much higher quality, unless its taken from another spacecraft, and then you're not likely to get the same effect. The ISS ones I think are a little more impressive because its bigger and there are a lot more details to make out.

Really this is about the best you can do for something like this. This looks to be right at the seeing limit (maybe doing it from a higher altitude could help), and theres plenty of light, so a bigger telescope isn't going to g

This photo is actually of comparable quality to what you'd get from NASA, given the same conditions under which it was taken under.

Bear in mind that the photo is being taken through many, many miles of air, during the daytime, and the daytime heat causes all kinds of instabilities in the air that will show up as waviness in the image (the same phenomenon causes stars to twinkle at night). Finding steady air at night is hard enough, but getting images this clear during the day is remarkable, even taking the quick shutter speed into account.

Also bear in mind that the Sun is only about 30 arcminutes across as seen from the Earth, meaning that the Shuttle silhouette itself is at most just a very few arcseconds in size. To put it in perspective, it's on the order of getting a clear photo of the text "In God We Trust" on a dime from the other end of a (US) football field while the dime is moving at 4 feet or so per second.

While I realize the difficulty of actually taking this picture, am I the only one who thinks this picture is actually really terrible quality? Or am I just used to much better quality from NASA photos?

They're up there to *fix* the hubble. They haven't actually fixed it yet...

west of vero beach is the stomping grounds of nasa engineers. I was in melbourne (like a 20 minute drive from vero beach) this past weekend and spoke with a few engineers who worked for nasa through contracts. That entire area is known as the "space coast". This was probably taken by an ex-nasa engineer or photographer. About month ago when I was up there was a rocket launch and there were probably 5-10 nasa guys in the street watching it. That area is absolutley saturated with guys who have an interest in nasa's activities and the professional know-how to do such things. While it could still be a hoax, there is nothing physically impossible and the location of origin of the photo only lends credibility.

west of vero beach is the stomping grounds of nasa engineers. I was in melbourne (like a 20 minute drive from vero beach) this past weekend and spoke with a few engineers who worked for nasa through contracts. That entire area is known as the "space coast". This was probably taken by an ex-nasa engineer or photographer. About month ago when I was up there was a rocket launch and there were probably 5-10 nasa guys in the street watching it. That area is absolutley saturated with guys who have an interest in nasa's activities and the professional know-how to do such things. While it could still be a hoax, there is nothing physically impossible and the location of origin of the photo only lends credibility.

Well, there you have it then. NASA at work. That's the agency that faked the moon landings, you know.

While driving through Florida a couple years ago, on vacation, I got lost. When I stopped by a Seven Eleven and asked where I was, and the guy answered "Melbourne", I promptly returned in the best Australian accent I could fake "I am sure I am still in Florida. It's very unlikely I could get that lost using a car".

The guy pointed my location on a map. 20 minutes later I was back to the hotel.

Of course it's a fake. The sky in the background is black, so obviously it's night, but for the sun to be out the sky would have to be blue. Duh!

(kidding of course. It's a fantastic picture and reminds me of how small we really are compared to the rest of the universe. Kind of like stepping into the Total Perspective Vortex except it doesn't fry your brain.)

It's a real photo, and it's not terribly difficult to take such photos if you have a good camera, a good telescope (Takahashi is among the best), and most importantly a good equatorial mount for the scope. For solar photos like this, add a good broadband solar filter into the mix.

Lock the scope onto the Sun, set the camera to capture frames as fast as possible, and then throw out everything that comes out crappy. There were two really good frames of the Atlantis shown, but there are no telling how many

You would also need to have up to date trajectory data on the shuttle and the ability to turn it into a findable 3D location. Consider the size of the orbiter in that image. If it deviates by 10 or 20 of its own diameters in any direction there will be no shot.

He has to find a spot on a line between the sun and the shuttle. If he goes up a mountain he has to go sideways to be back in the "beam" so to speak. If he sets up near a road he has to avoid being run over. If he sets up in a field he has to avoid

You don't really need full ephemeris data, you'd just need to know when the transit happened. I'll grant you determining when the transit happens is a more difficult problem, although you can pull the data off of the JPL HORIZONS http://ssd.jpl.nasa.gov/?horizons [nasa.gov] data.

Get two text files with a list of RA/DEC for the sun and Hubble for the next week, and set up a script to read through them and find the closest approach. If its less than the radius of the sun you have a winner. Given that this guy doe